Wnt7a deficit is associated with dysfunctional angiogenesis in pulmonary arterial hypertension.

INTRODUCTION: Pulmonary arterial hypertension (PAH) is characterised by loss of microvessels. The Wnt pathways control pulmonary angiogenesis but their role in PAH is incompletely understood. We hypothesised that Wnt activation in pulmonary microvascular endothelial cells (PMVECs) is required for pulmonary angiogenesis, and its loss contributes to PAH. METHODS: Lung tissue and PMVECs from healthy and PAH patients were screened for Wnt production. Global and endothelial-specific Wnt7a -/- mice were generated and exposed to chronic hypoxia and Sugen-hypoxia (SuHx). RESULTS: Healthy PMVECs demonstrated >6-fold Wnt7a expression during angiogenesis that was absent in PAH PMVECs and lungs. Wnt7a expression correlated with the formation of tip cells, a migratory endothelial phenotype critical for angiogenesis. PAH PMVECs demonstrated reduced vascular endothelial growth factor (VEGF)-induced tip cell formation as evidenced by reduced filopodia formation and motility, which was partially rescued by recombinant Wnt7a. We discovered that Wnt7a promotes VEGF signalling by facilitating Y1175 tyrosine phosphorylation in vascular endothelial growth factor receptor 2 (VEGFR2) through receptor tyrosine kinase-like orphan receptor 2 (ROR2), a Wnt-specific receptor. We found that ROR2 knockdown mimics Wnt7a insufficiency and prevents recovery of tip cell formation with Wnt7a stimulation. While there was no difference between wild-type and endothelial-specific Wnt7a -/- mice under either chronic hypoxia or SuHx, global Wnt7a +/- mice in hypoxia demonstrated higher pulmonary pressures and severe right ventricular and lung vascular remodelling. Similar to PAH, Wnt7a +/- PMVECs exhibited an insufficient angiogenic response to VEGF-A that improved with Wnt7a. CONCLUSIONS: Wnt7a promotes VEGF signalling in lung PMVECs and its loss is associated with an insufficient VEGF-A angiogenic response. We propose that Wnt7a deficiency contributes to progressive small vessel loss in PAH.

Novel Mechanisms Targeted by Drug Trials in Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is a rare disease associated with abnormally elevated pulmonary pressures and right heart failure resulting in high morbidity and mortality. Although the prognosis for patients with PAH has improved with the introduction of pulmonary vasodilators, disease progression remains a major problem. Given that available therapies are inadequate for preventing small-vessel loss and obstruction, there is active interest in identifying drugs capable of targeting angiogenesis and mechanisms involved in the regulation of cell growth and fibrosis. Among the mechanisms linked to PAH pathogenesis, preclinical studies have identified promising compounds that are currently being tested in clinical trials. These drugs target seven of the major mechanisms associated with PAH pathogenesis: bone morphogenetic protein signaling, tyrosine kinase receptors, estrogen metabolism, extracellular matrix, angiogenesis, epigenetics, and serotonin metabolism. In this review, we discuss the preclinical studies that led to prioritization of these mechanisms, and discuss completed and ongoing phase 2/3 trials using novel interventions such as sotatercept, anastrozole, rodatristat ethyl, tyrosine kinase inhibitors, and endothelial progenitor cells, among others. We anticipate that the next generation of compounds will build on the success of the current standard of care and improve clinical outcomes and quality of life for patients with PAH.

Lung Pericytes in Pulmonary Vascular Physiology and Pathophysiology.

Pericytes are mesenchymal-derived mural cells localized within the basement membrane of pulmonary and systemic capillaries. Besides structural support, pericytes control vascular tone, produce extracellular matrix components, and cytokines responsible for promoting vascular homeostasis and angiogenesis. However, pericytes can also contribute to vascular pathology through the production of pro-inflammatory and pro-fibrotic cytokines, differentiation into myofibroblast-like cells, destruction of the extracellular matrix, and dissociation from the vessel wall. In the lung, pericytes are responsible for maintaining the integrity of the alveolar-capillary membrane and coordinating vascular repair in response to injury. Loss of pericyte communication with alveolar capillaries and a switch to a pro-inflammatory/pro-fibrotic phenotype are common features of lung disorders associated with vascular remodeling, inflammation, and fibrosis. In this article, we will address how to differentiate pericytes from other cells, discuss the molecular mechanisms that regulate the interactions of pericytes and endothelial cells in the pulmonary circulation, and the experimental tools currently used to study pericyte biology both in vivo and in vitro. We will also discuss evidence that links pericytes to the pathogenesis of clinically relevant lung disorders such as pulmonary hypertension, idiopathic lung fibrosis, sepsis, and SARS-COVID. Future studies dissecting the complex interactions of pericytes with other pulmonary cell populations will likely reveal critical insights into the origin of pulmonary diseases and offer opportunities to develop novel therapeutics to treat patients afflicted with these devastating disorders. © 2021 American Physiological Society. Compr Physiol 11:2227-2247, 2021.

Novel TNIP2 and TRAF2 Variants Are Implicated in the Pathogenesis of Pulmonary Arterial Hypertension.

Background: Pulmonary arterial hypertension (PAH) is a rare disease characterized by pulmonary vascular remodeling and right heart failure. Specific genetic variants increase the incidence of PAH in carriers with a family history of PAH, those who suffer from certain medical conditions, and even those with no apparent risk factors. Inflammation and immune dysregulation are related to vascular remodeling in PAH, but whether genetic susceptibility modifies the PAH immune response is unclear. TNIP2 and TRAF2 encode for immunomodulatory proteins that regulate NF-κB activation, a transcription factor complex associated with inflammation and vascular remodeling in PAH. Methods: Two unrelated families with PAH cases underwent whole-exome sequencing (WES). A custom pipeline for variant prioritization was carried out to obtain candidate variants. To determine the impact of TNIP2 and TRAF2 in cell proliferation, we performed an MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay on healthy lung pericytes transfected with siRNA specific for each gene. To measure the effect of loss of TNIP2 and TRAF2 on NF-kappa-beta (NF-κB) activity, we measured levels of Phospho-p65-NF-κB in siRNA-transfected pericytes using western immunoblotting. Results: We discovered a novel missense variant in the TNIP2 gene in two affected individuals from the same family. The two patients had a complex form of PAH with interatrial communication and scleroderma. In the second family, WES of the proband with PAH and primary biliary cirrhosis revealed a de novo protein-truncating variant in the TRAF2. The knockdown of TNIP2 and TRAF2 increased NF-κB activity in healthy lung pericytes, which correlated with a significant increase in proliferation over 24 h. Conclusions: We have identified two rare novel variants in TNIP2 and TRAF2 using WES. We speculate that loss of function in these genes promotes pulmonary vascular remodeling by allowing overactivation of the NF-κB signaling activity. Our findings support a role for WES in helping identify novel genetic variants associated with dysfunctional immune response in PAH.

Diagnosis and Management of Pulmonary Hypertension in the Modern Era: Insights from the 6th World Symposium.

The past 20 years have seen major advances in the diagnosis and management of pulmonary hypertension, a disease associated with significant morbidity and mortality. The 6th World Symposium in Pulmonary Hypertension (WSPH) took place in February 2018 and attempted to consolidate the current knowledge in the field into practical recommendations to help prioritize an action plan to improve patient outcomes and identify future research directions. In this review, we will summarize the highlights of the 6th WSPH proceedings, including revisions to the hemodynamic definitions and classification of the various types of pulmonary hypertension, genetic advances, approaches to risk stratification, and updated treatment algorithms.

The 6th World Symposium on Pulmonary Hypertension: what's old is new.

In February 2018, the 6th World Symposium on Pulmonary Hypertension (WSPH) brought together experts from various disciplines to review the most relevant clinical and scientific advances in the field of PH over the last 5 years. Based on careful review and discussions by members of the different task forces, major revisions were made on the hemodynamic definition for various forms of PH and new genes were added to the list of genetic markers associated with pulmonary arterial hypertension (PAH) and pulmonary veno-occlusive disease. In addition, the use of risk stratification tools was encouraged as a strategy to reduce one-year mortality risk in PAH patients through early implementation of PAH therapies. While members of the medical community are still debating some of the proposed changes, the new WSPH guidelines advocate early diagnosis and initiation of combination therapy to reduce mortality and improve quality of life in patients with PH.